Low Profile Multi-Anode Assembly

ABSTRACT

A capacitor assembly configured to effectively dissipate heat when exposed to a high ripple current is provided. The assembly includes a plurality of capacitor elements, each including an anode body and lead, a dielectric layer overlying the anode body, and a solid electrolyte. Each capacitor element is defined by upper and lower major surfaces, first opposing minor surfaces, and second opposing minor surfaces. The major surfaces each have a surface area greater than that of each of the minor opposing surfaces. A hermetically sealed housing having a length, width, and height defines an interior cavity within which the plurality of capacitor elements are positioned. The ratio of the length to the height ranges from about 2 to about 80. Further, the lower major face of each capacitor element faces a lower wall of the housing, where the lower wall is defined by the housing&#39;s length and width.

BACKGROUND OF THE INVENTION

Many specific aspects of capacitor design have been a focus forimproving the performance characteristics of capacitors used inelectronic circuits in extreme environments such as automobileapplications including, for example, antilock braking systems, enginesystems, airbags, cabin entertainment systems, etc. Solid electrolyticcapacitors (e.g., tantalum capacitors) have been a major contributor tothe miniaturization of electronic circuits and have made possible theapplication of such circuits in extreme environments. Conventional solidelectrolytic capacitors may be formed by pressing a metal powder (e.g.,tantalum) around a metal lead wire, sintering the pressed part,anodizing the sintered anode, and thereafter applying a solidelectrolyte to form a capacitor element. In automotive applications, acapacitor assembly may need to have a high capacitance (e.g., about 100microFarads to about 500 microFarads), operate at high voltages (e.g.,about 50 volts to about 150 volts), and sustain exposure to hightemperatures (e.g., about 100° C. to about 150° C.) and high ripplecurrents (e.g., about 25 Amps to about 100 Amps) without failing.Because exposure of the capacitor assembly to a high ripple current canlead to high temperatures within the capacitor assembly, the capacitorassembly can be damaged and its reliability reduced if it is not able toadequately dissipate heat. This problem is compounded when multiplecapacitor elements are utilized in order to form a capacitor assemblywith a high enough capacitance. As such, attempts have been made tolower the equivalent series resistance (ESR) of capacitor assembliesthat include multiple capacitor elements, as a reduced ESR correspondswith the ability of the capacitor assembly to dissipate heat that isproduced when the capacitor assembly is exposed to high ripple currents.

Nevertheless, a need currently exists for a capacitor assembly havingimproved ESR and heat dissipation capabilities when exposed to highripple current environments and that can also operate reliably at hightemperatures and voltages, particularly when the capacitor assemblyincludes multiple capacitor elements.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, a capacitorassembly is disclosed. The capacitor assembly includes a plurality ofcapacitor elements that each contain a sintered porous anode body, adielectric layer that overlies the anode body, and a solid electrolyteoverlying the dielectric layer. An anode lead extends from eachcapacitor element, and each capacitor element is defined by upper andlower major surfaces, first opposing minor surfaces, and second opposingminor surfaces. The upper and lower major surfaces each have a surfacearea that is greater than a surface area of each of the minor opposingsurfaces.

The capacitor assembly also includes a housing having a length, a width,and a height, wherein the ratio of the length to the height ranges fromabout 2 to about 80. The housing is hermetically sealed and defines aninterior cavity. The plurality of capacitor elements are positionedwithin the interior cavity, wherein the lower major face of eachcapacitor element faces a lower wall of the housing, further wherein thelower wall is defined by the length and the width of the housing.

The capacitor assembly further includes an external anode terminationthat is in electrical connection with the anode lead of each capacitorelement and an external cathode termination that is in electricalconnection with the solid electrolyte of each capacitor element.

Other features and aspects of the present invention are set forth ingreater detail below.

BRIEF DESCRIPTION OF THE DRAWING

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth more particularly in the remainder of the specification, whichmakes reference to the appended figure in which:

FIG. 1 is a perspective view of one embodiment of the capacitor assemblyof the present invention;

FIG. 2 is a bottom view of another embodiment of the capacitor assemblyof the present invention;

FIG. 3 is a perspective view of one of the plurality of capacitorelements used in the capacitor assembly of the present invention;

FIG. 4 is a top view of one embodiment of the capacitor assembly of thepresent invention;

FIG. 5 is a top view of another embodiment of the capacitor assembly ofthe present invention;

FIG. 6 is a top view of another embodiment of the capacitor assembly ofthe present invention;

FIG. 7 is a bottom view of one embodiment of the housing of thecapacitor assembly of FIGS. 4-5, showing the external anode and cathodeterminations;

FIG. 8 is a bottom view of one embodiment of the housing of thecapacitor assembly of FIG. 6, showing the external anode and cathodeterminations; and

FIG. 9 is a perspective view of one embodiment of the capacitor assemblyof the present invention, where the lid has been removed to show anoptional encapsulant material that encapsulates at least a portion ofthe capacitor elements inside the housing.

Repeat use of references characters in the present specification anddrawing is intended to represent same or analogous features or elementsof the invention.

DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

It is to be understood by one of ordinary skill in the art that thepresent discussion is a description of exemplary embodiments only, andis not intended as limiting the broader aspects of the presentinvention, which broader aspects are embodied in the exemplaryconstruction.

Generally speaking, the present invention is directed to a low profilecapacitor assembly including a housing within which are contained aplurality of capacitor elements for use under extreme conditions, wherethe capacitor assembly may need to withstand ripple currents as high as100 Amps, may experience temperatures of 100° C. or more, and may beused in high voltage environments, such as at rated voltages of about 50volts or more. The capacitor assembly is low profile in that the ratioof the length of the housing to the height of the housing ranges fromabout 2 to about 80. To help achieve good performance under theaforementioned conditions, a variety of aspects of the assembly arecontrolled in the present invention, including the number of capacitorelements, the manner in which the capacitor elements are arranged andincorporated into the assembly, and the manner in which the capacitorelements are formed. For example, to help reduce the ESR of the assemblyso that the assembly has improved heat dissipation capabilities whileincreasing overall capacitance, the capacitor elements can beelectrically connected in parallel. To further help improve the heatdissipation of the assembly, the plurality of capacitor elements arearranged within a housing to maximize the surface area contact betweenthe capacitor elements and the housing, such as at its lower walldefined by its length and width, which can result in a ratio of thetotal surface area of the major surface of the capacitor elements incontact with the housing to the volume of the housing that ranges fromabout 0.06 mm⁻¹ to about 0.3 mm⁻¹. Besides being connected and arrangedin the housing in a certain manner, such as being connected in parallelin one particular embodiment, the capacitor elements are also enclosedand hermetically sealed within the housing to limit the amount of oxygenand moisture supplied to the solid electrolyte of the capacitor element.Limiting the amount of oxygen and moisture supplied to the solidelectrolyte can help further reduce the ESR of the capacitor assembly,resulting in increased heat dissipation capabilities.

Various embodiments of the present invention will now be described inmore detail.

I. Capacitor Elements

A. Anode

The anode of each of the capacitor elements is generally formed from avalve metal powder. The powder may have a specific charge of from about2,000 microFarads*Volts per gram (“μF*V/g”) to about 500,000 μF*V/g. Asis known in the art, the specific charge may be determined bymultiplying capacitance by the anodizing voltage employed, and thendividing this product by the weight of the electrode body prior toanodization. In certain embodiments, the powder may have a high specificcharge, such as about 70,000 μF*V/g or more, in some embodiments about80,000 μF*V/g or more, in some embodiments about 90,000 μF*V/g or more,in some embodiments from about 100,000 to about 400,000 μF*V/g, and insome embodiments, from about 150,000 to about 350,000 μF*V/g. Of course,the powder may also have a low specific charge, such as about 70,000μF*V/g or less, in some embodiments about 60,000 μF*V/g or less, in someembodiments about 50,000 μF*V/g or less, in some embodiments from about2,000 to about 40,000 μF*V/g, and in some embodiments, from about 5,000to about 35,000 μF*V/g.

The powder may contain individual particles and/or agglomerates of suchparticles. Compounds for forming the powder include a valve metal (i.e.,metal that is capable of oxidation) or valve metal-based compound, suchas tantalum, niobium, aluminum, hafnium, titanium, alloys thereof,oxides thereof, nitrides thereof, and so forth. For example, the valvemetal composition may contain an electrically conductive oxide ofniobium, such as niobium oxide having an atomic ratio of niobium tooxygen of 1:1.0±1.0, in some embodiments 1:1.0±0.3, in some embodiments1:1.0±0.1, and in some embodiments, 1:1.0±0.05. For example, the niobiumoxide may be NbO_(0.7), NbO_(1.0), NbO_(1.1), and NbO₂. Examples of suchvalve metal oxides are described in U.S. Pat. No. 6,322,912 to Fife;U.S. Pat. No. 6,391,275 to Fife et alt; U.S. Pat. No. 6,416,730 to Fifeet al; U.S. Pat. No. 6,527,937 to Fife; U.S. Pat. No. 6,576,099 toKimmel, et al.; U.S. Pat. No. 6,592,740 to Fife. et al.; and U.S. Pat.No. 6,639,787 to Kimmel eta; and U.S. Pat. No. 7,220,397 to Kinmel, al.,as well as U.S. Patent Application Publication Nos. 2005/0019581 toSchnitter; 2005/0103638 to Schnitter, et al.; 2005/0013765 to Thomas, etal.

The powder may be formed using techniques known to those skilled in theart. A precursor tantalum powder, for instance, may be formed byreducing a tantalum salt (e.g., potassium fluotantalate (K₂TaF₇), sodiumfluotantalate (Na₂TaF₇), tantalum pentachloride (TaCl₅), etc.) with areducing agent (e.g., hydrogen, sodium, potassium, magnesium, calcium,etc.). Such powders may be agglomerated in a variety of ways, such asthrough one or multiple heat treatment steps at a temperature of fromabout 700° C. to about 1400° C., in some embodiments from about 750° C.to about 1200° C., and in some embodiments, from about 800° C. to about1100° C. Heat treatment may occur in an inert or reducing atmosphere.For example, heat treatment may occur in an atmosphere containinghydrogen or a hydrogen-releasing compound (e.g., ammonium chloride,calcium hydride, magnesium hydride, etc.) to partially sinter the powderand decrease the content of impurities (e.g., fluorine). If desired,agglomeration may also be performed in the presence of a gettermaterial, such as magnesium. After thermal treatment, the highlyreactive coarse agglomerates may be passivated by gradual admission ofair. Other suitable agglomeration techniques are also described in U.S.Pat. No. 6,576,038 to Rao; U.S. Pat. No. 6,238,456 to Wolf, et al.; U.S.Pat. No. 5,954,856 to Pathar et al.; U.S. Pat. No. 5,082,491 to Rerat;U.S. Pat. No. 4,555,268 to Getz; U.S. Pat. No. 4,483,819 to Albrecht etal.; U.S. Pat. No. 4,441,927 to Getz. et al.; and U.S. Pat. No.4,017,302 to Bates et al.

To facilitate the construction of the anode body, certain components mayalso be included in the powder. For example, the powder may beoptionally mixed with a binder and/or lubricant to ensure that theparticles adequately adhere to each other when pressed to form the anodebody. Suitable binders may include, for instance, poly(vinyl butyral);poly(vinyl acetate); poly(vinyl alcohol); poly(vinyl pyrollidone);cellulosic polymers, such as carboxymethylcellulose, methyl cellulose,ethyl cellulose, hydroxyethyl cellulose, and methylhydroxyethylcellulose; atactic polypropylene, polyethylene; polyethylene glycol(e.g., Carbowax from Dow Chemical Co.); polystyrene,poly(butadiene/styrene); polyamides, polyimides, and polyacrylamides,high molecular weight polyethers; copolymers of ethylene oxide andpropylene oxide; fluoropolymers, such as polytetrafluoroethylene,polyvinylidene fluoride, and fluoro-olefin copolymers; acrylic polymers,such as sodium polyacrylate, poly(lower alkyl acrylates), poly(loweralkyl methacrylates) and copolymers of lower alkyl acrylates andmethacrylates; and fatty acids and waxes, such as stearic and othersoapy fatty acids, vegetable wax, microwaxes (purified paraffins), etc.The binder may be dissolved and dispersed in a solvent. Exemplarysolvents may include water, alcohols, and so forth. When utilized, thepercentage of binders and/or lubricants may vary from about 0.1% toabout 8% by weight of the total mass. It should be understood, however,that binders and/or lubricants are not necessarily required in thepresent invention.

The resulting powder may be compacted to form a pellet using anyconventional powder press device. For example, a press mold may beemployed that is a single station compaction press containing a die andone or multiple punches. Alternatively, anvil-type compaction pressmolds may be used that use only a die and single lower punch. Singlestation compaction press molds are available in several basic types,such as cam, toggle/knuckle and eccentric/crank presses with varyingcapabilities, such as single action, double action, floating die,movable platen, opposed ram, screw, impact, hot pressing, coining orsizing. The powder may be compacted around an anode lead (e.g., tantalumwire). It should be further appreciated that the anode lead mayalternatively be attached (e.g., welded) to the anode body subsequent topressing and/or sintering of the anode body.

After compaction, any binder/lubricant may be removed by heating thepellet under vacuum at a certain temperature (e.g., from about 150° C.to about 500° C.) for several minutes. Alternatively, thebinder/lubricant may also be removed by contacting the pellet with anaqueous solution, such as described in U.S. Pat. No. 6,197,252 toBishop, et al. Thereafter, the pellet is sintered to form a porous,integral mass. For example, in one embodiment, the pellet may besintered at a temperature of from about 1200° C. to about 2000° C., andin some embodiments, from about 1500° C. to about 1800° C. under vacuumor an inert atmosphere. Upon sintering, the pellet shrinks due to thegrowth of bonds between the particles. The pressed density of the pelletafter sintering may vary, but is typically from about 2.0 to about 7.0grams per cubic centimeter, in some embodiments from about 2.5 to about6.5, and in some embodiments, from about 3.0 to about 6.0 grams percubic centimeter. The pressed density is determined by dividing theamount of material by the volume of the pressed pellet.

Although not required, the thickness of the anode body may be selectedto improve the electrical performance of the capacitor. For example, thethickness of the anode may be about 4 millimeters or less, in someembodiments, from about 0.05 to about 2 millimeters, and in someembodiments, from about 0.1 to about 1 millimeter. The shape of theanode may also be selected to improve the electrical properties of theresulting capacitor. For example, the anode may have a shape that iscurved, sinusoidal, rectangular, U-shaped, V-shaped, etc. The anode mayalso have a “fluted” shape in that it contains one or more furrows,grooves, depressions, or indentations to increase the surface to volumeratio to minimize ESR and extend the frequency response of thecapacitance. Such “fluted” anodes are described, for instance, in U.S.Pat. No. 6,191,936 to Webber, et al; U.S. Pat. No. 5,949,639 to Maeda,et al.; and U.S. Pat. No. 3,345,545 to Bourgault et al., as well as U.S.Patent Application Publication No. 2005/0270725 to Hahn, et al.

An anode lead may also be connected to the anode body that extends in alongitudinal direction therefrom. The anode lead may be in the form of awire, sheet, etc., and may be formed from a valve metal compound, suchas tantalum, niobium, niobium oxide, etc. Connection of the lead may beaccomplished using known techniques, such as by welding the lead to thebody or embedding it within the anode body during formation (e.g., priorto compaction and/or sintering).

B. Dielectric

A dielectric also overlies or coats the anode body of each of thecapacitor elements in the capacitor assembly. The dielectric may beformed by anodically oxidizing (“anodizing”) the sintered anode so thata dielectric layer is formed over and/or within the anode body. Forexample, a tantalum (Ta) anode body may be anodized to tantalumpentoxide (Ta₂O₅). Typically, anodization is performed by initiallyapplying a solution to the anode body, such as by dipping the anode bodyinto the electrolyte. A solvent is generally employed, such as water(e.g., deionized water). To enhance ionic conductivity, a compound maybe employed that is capable of dissociating in the solvent to form ions.Examples of such compounds include, for instance, acids, such asdescribed below with respect to the electrolyte. For example, an acid(e.g., phosphoric acid) may constitute from about 0.01 wt. % to about 5wt. %, in some embodiments from about 0.05 wt. % to about 0.8 wt. %, andin some embodiments, from about 0.1 wt. % to about 0.5 wt. % of theanodizing solution. If desired, blends of acids may also be employed.

A current is passed through the anodizing solution to form thedielectric layer. The value of the formation voltage manages thethickness of the dielectric layer. For example, the power supply may beinitially set up at a galvanostatic mode until the required voltage isreached. Thereafter, the power supply may be switched to apotentiostatic mode to ensure that the desired dielectric thickness isformed over the entire surface of the anode body. Of course, other knownmethods may also be employed, such as pulse or step potentiostaticmethods. The voltage at which anodic oxidation occurs typically rangesfrom about 4 to about 400 V, and in some embodiments, from about 9 toabout 200 V, and in some embodiments, from about 20 to about 150 V.During oxidation, the anodizing solution can be kept at an elevatedtemperature, such as about 30° C. or more, in some embodiments fromabout 40° C. to about 200° C., and in some embodiments, from about 50°C. to about 100° C. Anodic oxidation can also be done at ambienttemperature or lower. The resulting dielectric layer may be formed on asurface of the anode body and within its pores.

C. Solid Electrolyte

As indicated above, a solid electrolyte overlies the dielectric thatgenerally functions as the cathode for the capacitor. In someembodiments, the solid electrolyte may include a manganese dioxide. Ifthe solid electrolyte includes manganese dioxide, the manganese dioxidesolid electrolyte may, for instance, be formed by the pyrolyticdecomposition of manganous nitrate (Mn(NO₃)₂). Such techniques aredescribed, for instance, in U.S. Pat. No. 4,945,452 to Sturmer, et al.,which is incorporated herein in its entirety by reference thereto forall purposes.

In other embodiments, the solid electrolyte contains a conductivepolymer, which is typically π-conjugated and has electrical conductivityafter oxidation or reduction, such as an electrical conductivity of atleast about 1 μS/cm. Examples of such π-conjugated conductive polymersinclude, for instance, polyheterocycles (e.g., polypyrroles,polythiophenes, polyanilines, etc.), polyacetylenes, poly-p-phenylenes,polyphenolates, and so forth. In one embodiment, for example, thepolymer is a substituted polythiophene, such as those having thefollowing general structure:

wherein,

T is O or S;

D is an optionally substituted C₁ to C₅ alkylene radical (e.g.,methylene, ethylene, n-propylene, n-butylene, n-pentylene, etc.);

R₇ is a linear or branched, optionally substituted C₁ to C₁₈ alkylradical (e.g., methyl, ethyl, n- or iso-propyl, n-, iso-, sec- ortert-butyl, n-pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl,1-ethylpropyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl,2,2-dimethylpropyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl,n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-hexadecyl,n-octadecyl, etc.); optionally substituted C₅ to C₁₂ cycloalkyl radical(e.g., cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononylcyclodecyl, etc.); optionally substituted C₆ to C₁₄ aryl radical (e.g.,phenyl, naphthyl, etc.); optionally substituted C₇ to C₁₆ aralkylradical (e.g., benzyl, o-, m-, p-totyl, 2,3-, 2,4-, 2,5-, 2-6, 3-4-,3,5-xylyl, mesityl, etc.); optionally substituted C₁ to C₄ hydroxyalkylradical, or hydroxyl radical; and

q is an integer from 0 to 8, in some embodiments, from 0 to 2, and inone embodiment, 0; and

n is from 2 to 5,000, in some embodiments from 4 to 2,000, and in someembodiments, from 5 to 1,000. Example of substituents for the radicals“D” or “R₇” include, for instance, alkyl, cycloalkyl, aryl, aralkyl,alkoxy, halogen, ether, thioether, disulphide, sulfoxide, sulfone,sulfonate, amino, aldehyde, keto, carboxylic acid ester, carboxylicacid, carbonate, carboxylate, cyano, alkylsilane and alkoxysilanegroups, carboxylamide groups, and so forth.

Particularly suitable thiophene polymers are those in which “D” is anoptionally substituted C₂ to C₃ alkylene radical. For instance, thepolymer may be optionally substituted poly(3,4-ethylenedioxythiophene),which has the following general structure:

Methods for forming conductive polymers, such as described above, arewell known in the art. For instance, U.S. Pat. No. 6,987,663 to Merker,et al., describes various techniques for forming substitutedpolythiophenes from a monomeric precursor. The monomeric precursor may,for instance, have the following structure:

wherein,

T, D, R₇, and q are defined above. Particularly suitable thiophenemonomers are those in which “D” is an optionally substituted C₂ to C₃alkylene radical. For instance, optionally substituted3,4-alkylenedioxythiophenes may be employed that have the generalstructure:

wherein, R₇ and q are as defined above. In one particular embodiment,“q” is 0. One commercially suitable example of 3,4-ethylenedioxthiopheneis available from Heraeus Clevios under the designation Clevios™ M.Other suitable monomers are also described in U.S. Pat. No. 5,111,327 toBlohm, et al. and U.S. Pat. No. 6,635,729 to Groenendaal, et al.Derivatives of these monomers may also be employed that are, forexample, dimers or trimers of the above monomers. Higher molecularderivatives, i.e., tetramers, pentamers, etc. of the monomers aresuitable for use in the present invention. The derivatives may be madeup of identical or different monomer units and used in pure form and ina mixture with one another and/or with the monomers. Oxidized or reducedforms of these precursors may also be employed.

Various methods may be utilized to form the conductive polymer layer.For example, an in situ polymerized layer may be formed by chemicallypolymerizing monomers in the presence of an oxidative catalyst. Theoxidative catalyst typically includes a transition metal cation, such asiron(III), copper(II), chromium(VI), cerium(IV), manganese(IV),manganese(VII), or ruthenium(III) cations, and etc. A dopant may also beemployed to provide excess charge to the conductive polymer andstabilize the conductivity of the polymer. The dopant typically includesan inorganic or organic anion, such as an ion of a sulfonic acid. Incertain embodiments, the oxidative catalyst has both a catalytic anddoping functionality in that it includes a cation (e.g., transitionmetal) and an anion (e.g., sulfonic acid). For example, the oxidativecatalyst may be a transition metal salt that includes iron(II) cations,such as iron(III) halides (e.g., FeCl₃) or iron(III) salts of otherinorganic acids, such as Fe(ClO₄)₃ or Fe₂(SO₄)₃ and the iron(III) saltsof organic acids and inorganic acids comprising organic radicals.Examples of iron (III) salts of inorganic acids with organic radicalsinclude, for instance, iron(III) salts of sulfuric acid monoesters of C₁to C₂₀ alkanols (e.g., iron(III) salt of lauryl sulfate). Likewise,examples of iron(III) salts of organic acids include, for instance,iron(III) salts of C₁ to C₂₀ alkane sulfonic acids (e.g., methane,ethane, propane, butane, or dodecane sulfonic acid); iron (III) salts ofaliphatic perfluorosulfonic acids (e.g., trifluoromethane sulfonic acid,perfluorobutane sulfonic acid, or perfluorooctane sulfonic acid); iron(III) salts of aliphatic C₁ to C₂₀ carboxylic acids (e.g.,2-ethylhexylcarboxylic acid); iron (III) salts of aliphaticperfluorocarboxylic acids (e.g., trifluoroacetic acid or perfluorooctaneacid); iron (III) salts of aromatic sulfonic acids optionallysubstituted by C₁ to C₂₀ alkyl groups (e.g., benzene sulfonic acid,o-toluene sulfonic acid, p-toluene sulfonic acid, or dodecylbenzenesulfonic acid); iron (III) salts of cycloalkane sulfonic acids (e.g.,camphor sulfonic acid); and so forth. Mixtures of these above-mentionediron(III) salts may also be used. Iron(III)-p-toluene sulfonate,iron(III)-o-toluene sulfonate, and mixtures thereof, are particularlysuitable. One commercially suitable example of iron(III)-p-toluenesulfonate is available from Heraeus Clevios under the designationClevios™ C.

The oxidative catalyst and monomer may be applied either sequentially ortogether to initiate the polymerization reaction. Suitable applicationtechniques for applying these components include screen-printing,dipping, electrophoretic coating, and spraying. As an example, themonomer may initially be mixed with the oxidative catalyst to form aprecursor solution. Once the mixture is formed, it may be applied to theanode part and then allowed to polymerize so that a conductive coatingis formed on the surface. Alternatively, the oxidative catalyst andmonomer may be applied sequentially. In one embodiment, for example, theoxidative catalyst is dissolved in an organic solvent (e.g., butanol)and then applied as a dipping solution. The anode part may then be driedto remove the solvent therefrom. Thereafter, the part may be dipped intoa solution containing the monomer. Regardless, polymerization istypically performed at temperatures of from about −10° C. to about 250°C., and in some embodiments, from about 0° C. to about 200° C.,depending on the oxidizing agent used and desired reaction time.Suitable polymerization techniques, such as described above, may bedescribed in more detail in U.S. Pat. No. 7,515,396 to Biler. Stillother methods for applying such conductive coating(s) may be describedin U.S. Pat. No. 5,457,862 to Sakata, et al., U.S. Pat. No. 5,473,503 toSakata. et al., U.S. Pat. No. 5,729,428 to Sakata et al., and U.S. Pat.No. 5,812,367 to Kudoh, et al.

In addition to in situ application, the conductive polymer solidelectrolyte may also be applied in the form of a dispersion ofconductive polymer particles. One benefit of employing a dispersion isthat it may minimize the presence of ionic species (e.g., Fe²⁺ or Fe³⁺)produced during in situ polymerization, which can cause dielectricbreakdown under high electric field due to ionic migration. Thus, byapplying the conductive polymer as a dispersion rather through in situpolymerization, the resulting capacitor may exhibit a relatively high“breakdown voltage.” To enable good impregnation of the anode, theparticles employed in the dispersion typically have a small size, suchas an average size (e.g., diameter) of from about 1 to about 150nanometers, in some embodiments from about 2 to about 50 nanometers, andin some embodiments, from about 5 to about 40 nanometers. The diameterof the particles may be determined using known techniques, such as byultracentrifuge, laser diffraction, etc. The shape of the particles maylikewise vary. In one particular embodiment, for instance, the particlesare spherical in shape. However, it should be understood that othershapes are also contemplated by the present invention, such as plates,rods, discs, bars, tubes, irregular shapes, etc. The concentration ofthe particles in the dispersion may vary depending on the desiredviscosity of the dispersion and the particular manner in which thedispersion is to be applied to the capacitor. Typically, however, theparticles constitute from about 0.1 to about 10 wt. %, in someembodiments from about 0.4 to about 5 wt. %, and in some embodiments,from about 0.5 to about 4 wt. % of the dispersion.

The dispersion also generally contains a counterion that enhances thestability of the particles. That is, the conductive polymer (e.g.,polythiophene or derivative thereof) typically has a charge on the mainpolymer chain that is neutral or positive (cationic). Polythiophenederivatives, for instance, typically carry a positive charge in the mainpolymer chain. In some cases, the polymer may possess positive andnegative charges in the structural unit, with the positive charge beinglocated on the main chain and the negative charge optionally on thesubstituents of the radical “R”, such as sulfonate or carboxylategroups. The positive charges of the main chain may be partially orwholly saturated with the optionally present anionic groups on theradicals “R.” Viewed overall, the polythiophenes may, in these cases, becationic, neutral or even anionic. Nevertheless, they are all regardedas cationic polythiophenes as the polythiophene main chain has apositive charge.

The counterion may be a monomeric or polymeric anion that counteractsthe charge of the conductive polymer. Polymeric anions can, for example,be anions of polymeric carboxylic acids (e.g., polyacrylic acids,polymethacrylic acid, polymaleic acids, etc.); polymeric sulfonic acids(e.g., polystyrene sulfonic acids (“PSS”), polyvinyl sulfonic acids,etc.); and so forth. The acids may also be copolymers, such ascopolymers of vinyl carboxylic and vinyl sulfonic acids with otherpolymerizable monomers, such as acrylic acid esters and styrene.Likewise, suitable monomeric anions include, for example, anions of C₁to C₂₀ alkane sulfonic acids (e.g., dodecane sulfonic acid); aliphaticperfluorosulfonic acids (e.g., trifluoromethane sulfonic acid,perfluorobutane sulfonic acid or perfluorooctane sulfonic acid);aliphatic C₁ to C₂₀ carboxylic acids (e.g., 2-ethyl-hexylcarboxylicacid); aliphatic perfluorocarboxylic acids (e.g., trifluoroacetic acidor perfluorooctanoic acid); aromatic sulfonic acids optionallysubstituted by C₁ to C₂₀ alkyl groups (e.g., benzene sulfonic acid,o-toluene sulfonic acid, p-toluene sulfonic acid or dodecylbenzenesulfonic acid); cycloalkane sulfonic acids (e.g., camphor sulfonic acidor tetrafluoroborates, hexafluorophosphates, perchlorates,hexafluoroantimonates, hexafluoroarsenates or hexachloroantimonates);and so forth. Particularly suitable counteranions are polymeric anions,such as a polymeric carboxylic or sulfonic acid (e.g., polystyrenesulfonic acid (“PSS”)). The molecular weight of such polymeric anionstypically ranges from about 1,000 to about 2,000,000, and in someembodiments, from about 2,000 to about 500,000.

When employed, the weight ratio of such counterions to conductivepolymers in the dispersion and in the resulting layer is typically fromabout 0.5:1 to about 50:1, in some embodiments from about 1:1 to about30:1, and in some embodiments, from about 2:1 to about 20:1. The weightof the electrically conductive polymers corresponds referred to theabove-referenced weight ratios refers to the weighed-in portion of themonomers used, assuming that a complete conversion occurs duringpolymerization. In addition to conductive polymer(s) and counterion(s),the dispersion may also contain one or more binders, dispersion agents,fillers, adhesives, crosslinking agents, etc.

The polymeric dispersion may be applied using a variety of knowntechniques, such as by spin coating, impregnation, pouring, dropwiseapplication, injection, spraying, doctor blading, brushing, printing(e.g., ink-jet, screen, or pad printing), or dipping. Although it mayvary depending on the application technique employed, the viscosity ofthe dispersion is typically from about 0.1 to about 100,000 mPas(measured at a shear rate of 100 s⁻¹), in some embodiments from about 1to about 10,000 mPas, in some embodiments from about 10 to about 1,500mPas, and in some embodiments, from about 100 to about 1000 mPas. Onceapplied, the layer may be dried and/or washed. One or more additionallayers may also be formed in this manner to achieve the desiredthickness. Typically, the total thickness of the layer(s) formed by thisparticle dispersion is from about 1 to about 50 μm, and in someembodiments, from about 5 to about 20 μm. The weight ratio ofcounterions to conductive polymers is likewise from about 0.5:1 to about50:1, in some embodiments from about 1:1 to about 30:1, and in someembodiments, from about 2:1 to about 20:1.

If desired, a hydroxyl-functional nonionic polymer may also be includedin the solid electrolyte. The term “hydroxy-functional” generally meansthat the compound contains at least one hydroxyl functional group or iscapable of possessing such a functional group in the presence of asolvent. Without intending to be limited by theory, it is believed thathydroxy-functional nonionic polymers can improve the degree of contactbetween the conductive polymer and the surface of the internaldielectric, which is typically relatively smooth in nature as a resultof higher forming voltages. This unexpectedly increases the breakdownvoltage and wet-to-dry capacitance of the resulting capacitor.Furthermore, it is believed that the use of a hydroxy-functional polymerwith a certain molecular weight can also minimize the likelihood ofchemical decomposition at high voltages. For instance, the molecularweight of the hydroxy-functional polymer may be from about 100 to 10,000grams per mole, in some embodiments from about 200 to 2,000, in someembodiments from about 300 to about 1,200, and in some embodiments, fromabout 400 to about 800.

Any of a variety of hydroxy-functional nonionic polymers may generallybe employed for this purpose. In one embodiment, for example, thehydroxy-functional polymer is a polyalkylene ether. Polyalkylene ethersmay include polyalkylene glycols (e.g., polyethylene glycols,polypropylene glycols polytetramethylene glycols, polyepichlorohydrins,etc.), polyoxetanes, polyphenylene ethers, polyether ketones, and soforth. Polyalkylene ethers are typically predominantly linear, nonionicpolymers with terminal hydroxy groups. Particularly suitable arepolyethylene glycols, polypropylene glycols and polytetramethyleneglycols (polytetrahydrofurans), which are produced by polyaddition ofethylene oxide, propylene oxide or tetrahydrofuran onto water. Thepolyalkylene ethers may be prepared by polycondensation reactions fromdiols or polyols. The diol component may be selected, in particular,from saturated or unsaturated, branched or unbranched, aliphaticdihydroxy compounds containing to 36 carbon atoms or aromatic dihydroxycompounds, such as, for example, pentane-1,5-diol, hexane-1,6-diol,neopentyl glycol, bis-(hydroxymethyl)-cyclohexanes, bisphenol A, dimerdiols, hydrogenated dimer diols or even mixtures of the diols mentioned.In addition, polyhydric alcohols may also be used in the polymerizationreaction, including for example glycerol, di- and polyglycerol,trimethylolpropane, pentaerythritol or sorbitol.

In addition to those noted above, other hydroxy-functional nonionicpolymers may also be employed in the present invention. Some examples ofsuch polymers include, for instance, ethoxylated alkylphenols;ethoxylated or propoxylated C₆-C₂₄ fatty alcohols; polyoxyethyleneglycol alkyl ethers having the general formula:CH₃—(CH₂)₁₀₋₁₆—(O—C₂H₄)₁₋₂₅—OH (e.g., octaethylene glycol monododecylether and pentaethylene glycol monododecyl ether); polyoxypropyleneglycol alkyl ethers having the general formula:CH₃—(CH₂)₁₀₋₁₆—(O—C₃H₆)₁₋₂₅—OH; polyoxyethylene glycol octylphenolethers having the following general formula:C₈H₁₇—(C₆H₄)—(O—C₂H₄)₁₋₂₅—OH (e.g., Triton™ X-100); polyoxyethyleneglycol alkylphenol ethers having the following general formula:C₉H₁₉—(C₆H₄)—(O—C₂H₄)₁₋₂₅—OH (e.g., nonoxynol-9); polyoxyethylene glycolesters of C₈-C₂₄ fatty acids, such as polyoxyethylene glycol sorbitanalkyl esters (e.g., polyoxyethylene (20) sorbitan monolaurate,polyoxyethylene (20) sorbitan monopalmitate, polyoxyethylene (20)sorbitan monostearate, polyoxyethylene (20) sorbitan monooleate, PEG-20methyl glucose distearate, PEG-20 methyl glucose sesquistearate, PEG-80castor oil, and PEG-20 castor oil, PEG-3 castor oil, PEG 600 dioleate,and PEG 400 dioleate) and polyoxyethylene glycerol alkyl esters (e.g.,polyoxyethylene-23 glycerol laurate and polyoxyethylene-20 glycerolstearate); polyoxyethylene glycol ethers of C₈-C₂₄ fatty acids (e.g.,polyoxyethylene-10 cetyl ether, polyoxyethylene-10 stearyl ether,polyoxyethylene-cetyl ether, polyoxyethylene-10 oleyl ether,polyoxyethylene-20 oleyl ether, polyoxyethylene-20 isohexadecyl ether,polyoxyethylene-15 tridecyl ether, and polyoxyethylene-6 tridecylether); block copolymers of polyethylene glycol and polypropylene glycol(e.g., Poloxamers); and so forth, as well as mixtures thereof.

The hydroxy-functional nonionic polymer may be incorporated into thesolid electrolyte in a variety of different ways. In certainembodiments, for instance, the nonionic polymer may simply beincorporated into any conductive polymer layer(s) formed by a method asdescribed above (e.g., in situ polymerization or pre-polymerizedparticle dispersion). In other embodiments, however, the nonionicpolymer may be applied after the initial polymer layer(s) are formed.

D. External Polymer Coating

Although not required, an external polymer coating may be applied to theanode body and overlie the solid electrolyte of each of the capacitorelements in the capacitor assembly. The external polymer coatinggenerally contains one or more layers formed from a dispersion ofpre-polymerized conductive particles, such as described in more detailabove. The external coating may be able to further penetrate into theedge region of the capacitor body to increase the adhesion to thedielectric and result in a more mechanically robust part, which mayreduce equivalent series resistance and leakage current. If desired, acrosslinking agent may also be employed in the external polymer coatingto enhance the degree of adhesion to the solid electrolyte. Typically,the crosslinking agent is applied prior to application of the dispersionused in the external coating. Suitable crosslinking agents aredescribed, for instance, in U.S. Patent Publication No. 2007/0064376 toMerker, et al. and include, for instance, amines (e.g., diamines,triamines, oligomer amines, polyamines, etc.); polyvalent metal cations,such as salts or compounds of Mg, Al, Ca, Fe, Cr, Mn, Ba, Ti, Co, Ni,Cu, Ru, Ce or Zn, phosphonium compounds, sulfonium compounds, etc.

E. Other Components of the Capacitor Elements

If desired, the capacitor elements may also contain other layers as isknown in the art. For example, a protective coating may optionally beformed between the dielectric and solid electrolyte, such as one made ofa relatively insulative resinous material (natural or synthetic), suchas shellac resins. These and other protective coating materials aredescribed in more detail U.S. Pat. No. 6,674,635 to Fife, et al. Ifdesired, the part may also be applied with a carbon layer (e.g.,graphite) and silver layer, respectively. The silver coating may, forinstance, act as a solderable conductor, contact layer, and/or chargecollector for the capacitor and the carbon coating may limit contact ofthe silver coating with the solid electrolyte. Such coatings may coversome or all of the solid electrolyte.

Regardless of the various components used to form each of the pluralityof capacitor elements, as shown in FIG. 3, each capacitor element 20 canhave a length L₂ in the −x direction ranging from about 3 millimeters toabout 6 millimeters, such as from about 3.5 millimeters to about 5.5millimeters, such as from about 4 millimeters to about 5 millimeters, awidth W₂ in the −y direction ranging from about 2 millimeters to about10 millimeters, such as from about 2.5 millimeters to about 8millimeters, such as from about 3 millimeters to about 6 millimeters,and a height H₂ in the −z direction ranging from about 0.5 millimetersto about 5 millimeters, such as from about 1.25 millimeters to about 4millimeters, such as from about 1.5 millimeters to about 3 millimeters.Further, each capacitor element 20 can include opposing major surfaces23 a and 23 b, first opposing minor surfaces 25 a and 25 b, and secondopposing minor surfaces 27 a and 27 b. The term major surface isintended to mean a surface of the capacitor element 20 having a largersurface area than the other surfaces (i.e., minor surfaces) of thecapacitor element. As shown, the anode lead 6 can extend from one of thesecond opposing minor surfaces 27 b, although it is to be understoodthat the anode lead 6 can extend from the other opposing minor surface27 a or one of first opposing minor surfaces 25 a and 25 b. In someembodiments and depending on the particular arrangement and size of thecapacitor elements 20 utilized in the capacitor assembly of the presentinvention, the surface area of one of the opposing major surfaces 23 aor 23 b (e.g., the upper major surface 23 a or the lower major surface23 b) for each capacitor element 20 can range from about 10 mm² to about45 mm², such as from about 12.5 mm² to about 40 mm², such as from about15 mm² to about 30 mm². Meanwhile, referring to FIGS. 3-6, in someembodiments, the total surface area of all of the lower opposing majorsurfaces 23 b of the capacitor elements 20(1)-20(40) that are in contactwith the lower wall 123 of the casing can range from about 600 mm² toabout 1200 mm², such as from about 700 mm² to about 1100 mm², such asfrom about 800 mm² to about 1000 mm².

II. Housing

As indicated above, a plurality of capacitor elements are hermeticallysealed within a housing to form the capacitor assembly of the presentinvention. The number of capacitor elements heremetically sealed withinthe housing can range from about 2 to about 200, such as from about 10to about 100, such as from about 20 to about 50. Hermetic sealing can,in some embodiments, occur in the presence of a gaseous atmosphere thatcontains at least one inert gas so as to inhibit oxidation of the solidelectrolyte during use. The inert gas may include, for instance,nitrogen, helium, argon, xenon, neon, krypton, radon, and so forth, aswell as mixtures thereof. Typically, inert gases can constitute themajority of the atmosphere within the housing, such as from about 50 wt.% to 100 wt. %, in some embodiments from about 75 wt. % to 100 wt. %,and in some embodiments, from about 90 wt. % to about 99 wt. % of theatmosphere. If desired, a relatively small amount of non-inert gases mayalso be employed, such as carbon dioxide, oxygen, water vapor, etc. Insuch cases, however, the non-inert gases typically constitute 15 wt. %or less, in some embodiments 10 wt. % or less, in some embodiments about5 wt. % or less, in some embodiments about 1 wt. % or less, and in someembodiments, from about 0.01 wt. % to about 1 wt. % of the atmospherewithin the housing. For example, the moisture content (expressed interms of relatively humidity) may be about 10% or less, in someembodiments about 5% or less, in some embodiments about 1% or less, andin some embodiments, from about 0.01 to about 5%.

Any of a variety of different materials may be used to form the housing,such as metals, plastics, ceramics, and so forth. In one embodiment, forexample, the housing includes one or more layers of a metal, such astantalum, niobium, aluminum, nickel, hafnium, titanium, copper, silver,steel (e.g., stainless), alloys thereof (e.g., electrically conductiveoxides), composites thereof (e.g., metal coated with electricallyconductive oxide), and so forth. In another embodiment, the housing mayinclude one or more layers of a ceramic material, such as aluminumnitride, aluminum oxide, silicon oxide, magnesium oxide, calcium oxide,glass, etc., as well as combinations thereof. The thickness or height ofthe housing is generally selected to minimize the thickness or height ofthe low profile capacitor assembly. For instance, referring to FIG. 1,the height H₁ of the housing in the −z direction can range from about 1millimeter to about 20 millimeters, such as from about 2 millimeters toabout 10 millimeters, such as from about 3 millimeters to about 6millimeters. Meanwhile, the length L₁ of the housing in the −x directionmay range from about 20 millimeters to about 100 millimeters, such asfrom about 40 millimeters to 70 millimeters, such as from about 45millimeters to about 65 millimeters, and the width W₁ of the housing inthe −y direction may range from about 10 millimeters to about 60millimeters, such as from about 20 millimeters to about 50 millimeters,such as from about 25 millimeters to about 45 millimeters. Further, insome embodiments, the housing can have a volume ranging from about 7000mm³ to about 12,000 mm³, such as from about 7500 mm³ to about 11,500mm³, such as from about 8000 mm³ to about 11,000 mm³. Moreover, thehousing can have a low profile such that the ratio of the length L₁ ofthe housing in the −x direction to the height H₁ of the housing in the−z direction is at least about 2. For instance, the ratio of the lengthL₁ to the height H₁ can range from about 2 to about 80, such as fromabout 4 to about 60, such as from about to about 40.

The plurality of capacitor elements may be attached to the housing usingany of a variety of different techniques. Although by no means required,the capacitor elements may be attached to the housing in such a mannerthat anode and cathode terminations are formed external to the housingfor subsequent integration into a circuit. The particular configurationof the terminations may depend on the intended application. In oneembodiment, for example, the capacitor assembly may be formed so that itis surface mountable, and yet still mechanically robust. For example,the anode leads and the cathodes of the capacitor elements may beelectrically connected to external, surface mountable terminations(e.g., pads, sheets, plates, frames, etc.), which may extend through thehousing to connect with the anode of the capacitor element through ananode lead frame, such as through a conductive member, plating layer,solder pad, etc. as discussed in more detail below, and which may extendthrough the housing to connect with the cathode through a plating layer.In another embodiment, the anode lead and the cathode of the capacitorelement may be directly electrically connected to external, surfacemountable terminations (e.g., pads, sheets, plates, frames, etc.), whichmay extend through the housing to connect with the cathodes and with theanode leads.

The thickness or height of the external terminations is generallyselected to minimize the thickness of the capacitor assembly. Forinstance, the thickness of the terminations may range from about 0.05millimeters to about 1 millimeter, such as from about 0.05 millimetersto about 0.5 millimeters, such as from about 0.1 millimeters to about0.2 millimeters. If desired, the surface of the terminations may beelectroplated with nickel, silver, gold, tin, cobalt, etc. or alloysthereof as is known in the art to ensure that the final part ismountable to the circuit board. In one particular embodiment, thetermination(s) are deposited with nickel and silver flashes,respectively, and the mounting surface is also plated with a tin solderlayer. In another embodiment, the termination(s) are deposited with thinouter metal layers (e.g., gold) onto a base metal layer (e.g., copperalloy) to further increase conductivity.

Referring to FIGS. 1-2 and 4, for example one particular embodiment of acapacitor assembly 100 is shown that contains 40 capacitor elementsdisposed inside a housing and arranged in multiple parallel rows (e.g.,rows 1-4), where each row of 10 capacitor elements extends in alongitudinal direction L_(G) along the length L₁ of the housing.However, it is to be understood that any number of capacitor elementscan be in each row, and any number of rows can be utilized depending onthe particular requirements of the capacitor assembly. As shown, thehousing of the capacitor assembly 100 includes a lower wall 123 andopposing sidewalls 124 and 125 between which a cavity 526 is formed thatincludes forty capacitor elements 20(1)-20(40). The lower wall 123 andsidewalls 124 and 125 may be formed from one or more layers of a metal,plastic, or ceramic material such as described above. The capacitorelements 20(1)-20(40) are arranged in parallel inside the cavity 526 ofthe housing, where such parallel arrangement helps to reduce the ESR ofthe capacitor element 100, where the reduced ESR contributes to theability of the capacitor assembly 100 to dissipate heat effectively.

In the embodiments of FIGS. 4-6, the capacitor elements 20(1)-20(40) arealigned so that the minor surface 25 b of one capacitor element (e.g.,capacitor element 20(1)) is positioned adjacent and faces the minorsurface 25 a of its neighboring capacitor element (e.g., capacitorelement 20(2)). Meanwhile, the lower major surface 23 b (see FIG. 3) ofeach of the capacitor elements 20(1)-20(40) faces the lower wall 123 ofthe housing and is in contact with the lower wall 123, such as via aplating layer as discussed in more detail below, where arranging thecapacitor elements 20(1)-(40) so that their lower major surfaces 23 bare in contact with the lower wall 123 rather than their minor opposingsurfaces 25 a, 25 b, 27 a, and 27 b (see FIG. 3) increases the surfacearea of the capacitor elements 20(1)-20(40) that are in contact with thecasing, which further contributes to the ability of the capacitorassembly 100 to dissipate heat effectively. The ability of the capacitorassembly of the present invention to dissipate heat can be expressed interms of the ratio of the total surface area of the lower major surfacesof the capacitor elements in contact with the casing via the platinglayer to the volume of the housing, where a ratio greater than about0.05 mm⁻¹ can be associated with an increased ability of the capacitorassembly to dissipate heat. For instance, the ratio of the total surfacearea of the lower major surfaces of the capacitor elements in contactwith the casing through the plating layer to the volume of the housingcan be greater than about 0.06 mm⁻¹ and can range, in some embodiments,from about 0.06 mm⁻¹ to about 0.3 mm⁻¹, such as from about 0.065 mm⁻¹ toabout 0.25 mm⁻¹, such as from about 0.07 mm⁻¹ to about 0.20 mm⁻¹, suchas from about 0.075 mm⁻¹ to about 0.15 mm⁻¹.

As described above and as shown in FIGS. 1-2, the capacitor assembly 100may also contain an external anode termination 135 and an externalcathode termination 137 to which the anode lead 6 and the solidelectrolyte/cathode on the lower major surface 23 b of each of thecapacitor elements 20(1)-20(40) are electrically connected in parallel.Further, lead frames and plating layers may be employed within theinterior cavity of the housing to facilitate the formation of theexternal terminations 135 and 137 in a mechanically stable manner. Forexample, referring to FIG. 4, the capacitor assembly 100 may include ananode lead frame that has a first planar and a second portion 67 that is“upstanding” in the sense that it is provided in a plane that isgenerally perpendicular to the direction in which the anode lead 6 ofeach capacitor element 20(1)-20(40) extends. In this manner, the secondportion 67 can limit movement of the lead 6 to enhance surface contactand mechanical stability during use. Further, if desired, an insulativematerial 7 (e.g., Teflon™ washer) may be employed around the lead 6. Thesecond portion 67 may possess a mounting region (not shown) that isconnected to the anode lead 6. The region may have a “U-shape” forfurther enhancing surface contact and mechanical stability of the lead6. Moreover, the anode lead 6 can be connected to the second portion 67of the anode lead frame via laser welding, resistance welding, aconductive adhesive, or any other suitable method.

For example, an anode lead frame that can include a first portion 65 a,65 b, 65 c, and 65 d for each row of capacitor elements and forty secondportions 67(1)-67(40) (labeled as 67 for simplicity) corresponding witheach of the 40 capacitor elements may be employed to connect the fourrows of 10 capacitor elements (e.g., row 1 including capacitor elements20(1)-20(10) connected to the anode lead frame via their anode leads 6at second portion 67(1)-(10); row 2 including capacitor elements20(11)-20(20) connected to the anode lead frame via their anode leads 6at second portion 67(11)-67(20); row 3 including capacitor elements20(21)-20(30) connected to anode lead frame component 65 c via theiranode leads 6 at second portion 67(21)-67(30); and row 4 includingcapacitor elements 20(31)-20(40) connected to the anode lead frame viatheir anode leads 6 at second portion 67(31)-67(40)). Further, althoughnot shown, if desired, the first portions 65 b and 65 c of the anodelead frame associated with rows 2 and 3 may be combined into a singlefirst portion of the anode lead frame as the capacitor elements20(11)-20(20) and 20(21)-20(30) are positioned such that their anodeleads 6 face each other. As discussed above, in one particularembodiment, each anode lead 6 is laser welded to each second portion 67of the anode lead frame. However, it is also to be understood that thesecomponents can be connected via resistance welding, a conductiveadhesive, etc. Meanwhile, in one particular embodiment, the firstportions 65 a-65 d of the anode lead frame can be connected to the lowerwall 123 of the housing via resistance welding. However, it is also tobe understood that any other suitable method can be used as well, suchas connecting the first portions 65 a-65 d to the lower wall 123 of thehousing via a conductive adhesive.

Further, the surfaces of the anode lead frame first portions 65 a-65 dand second portions 67(1)-67(40) may be electroplated with nickel,silver, gold, tin, cobalt, etc. or allows thereof as is known in the artto ensure adequate connection to the capacitor elements 20(1)-20(40) viathe anode lead 6 and to the lower wall 123 of the housing. In oneparticular embodiment, the anode lead frame can be deposited with nickeland silver flashes, respectively, and the mounting surface can alsoplated with a tin solder layer. In another embodiment, the anode leadframe can be deposited with thin outer metal layers (e.g., gold) onto abase metal layer (e.g., copper alloy) to further increase conductivity.In still another embodiment, strips of a nickel-iron alloy (e.g., NILO®strips) or strips of any other suitable metal material (not shown) canbe soldered onto a lower wall 123 of the housing beneath the firstportions 65 a-65 b of the anode lead frame.

In addition, various components may also be employed to connect the fourrows of 10 capacitor elements to the lower wall 123 of the housing(e.g., row 1 including capacitor elements 20(1)-20(10) connected to thelower wall 123 at their lower major surfaces 23 b; row 2 includingcapacitor elements 20(11)-20(20) connected to lower wall 123 at theirlower major surfaces 23 b; row 3 including capacitor elements20(21)-20(30) connected to the lower wall 123 at their lower majorsurfaces 23 b; and row 4 including capacitor elements 20(31)-20(40)connected to the lower wall 123 at their lower major surfaces 23 b). Inone embodiment, for example, the lower major surfaces 23 b of thecapacitor elements 20(1)-20(40) can be connected to the lower wall 123of the housing via a conductive adhesive (not shown), where the lowerwall 123 includes four rows of metal plating layers 29 a, 29 b, 29 c,and 29 d. The metal plating layers 29 a, 29 b, 29 c, and 29 d can beformed of any suitable metal, and, in one particular embodiment, can benickel plating layers.

As mentioned above, it is to be understood that attachment of thecapacitor elements, either on the anode side or cathode side, maygenerally be accomplished using any of a variety of known techniques,such as welding, laser welding, conductive adhesives, etc. Whenemployed, conductive adhesives may be formed from conductive metalparticles contained with a resin composition. The metal particles may besilver, copper, gold, platinum, nickel, zinc, bismuth, etc. The resincomposition may include a thermoset resin (e.g., epoxy resin), curingagent (e.g., acid anhydride), and coupling agent (e.g., silane couplingagents). Suitable conductive adhesives are described in U.S. PatentApplication Publication No. 2006/0038304 to Osako, et al.

In addition, as shown in FIG. 5, to further enhance the ability of thecapacitor assembly to dissipate heat, the capacitor assembly can includeother components. For instance, capacitor element 200 includes metalstrips 133 in the −y direction and metal strips 131 in the −x directionthat are in contact with the upper major surfaces 23 a of severalcapacitor elements 20. The metal material can be copper or any otherheat dissipating material and serves to further increase the surfacearea available for the dissipation of heat.

Turning now to FIG. 6, a capacitor assembly 300 having an arrangementalternative to that shown in FIGS. 4-5 is illustrated, where the anodeleads 6 associated with the capacitor elements 20(1)-20(10) in row 1 and20(11)-20(20) in row 2 as defined above face each other, allowing forthe combination of the first portions 65 a and 65 b of the anode leadframe for rows 1 and 2 to be combined into a single component ifdesired. Similarly, the anode leads 6 associated with capacitor elements20(21)-20(30) in row 3 and 20(31)-20(40) in row 4 as defined above faceeach other, allowing for the combination of the first portions 65 c and65 d of the anode lead frame for rows 1 and 2 to be combined into asingle component if desired. Further, the upper major faces 23 a of thecapacitor elements of rows 2 and 3 as defined above are adjacent eachother, allowing for the combination of plating layers 29 b and 29 c intoa single component if desired.

As discussed above, the capacitor assembly contains an anode termination135 and a cathode termination 137, which may be external to the housingand formed from separate plates, sheets, etc. Further, such terminationscan be connected to the anode lead frame and cathode plating layer/metalstrip (e.g., NILO® strip) components via conductive traces that extendthrough the lower wall 123 of the housing. Referring to FIG. 7 for thecapacitor element arrangement of FIGS. 4-5 and FIG. 8 for the capacitorelement arrangement of FIG. 6, because the first portions 65 a-65 d ofthe anode lead frame and the metal plating layers 29 a-29 d extend thelength L₁ and width W₁ of the casing of the capacitor assembly 100, theconductive traces 139 to connect the first portions 65 a-65 d of theanode lead frame to the external anode termination 135 are formed onlythrough the part of the lower wall 123 of the casing disposedimmediately above external anode termination 135 and immediately belowthe first portions 65 a-65 d of the anode lead frame component, whilethe conductive traces 141 to connect the metal plating layers 29 a-29 dto the external cathode termination 137 are formed only through the partof the lower wall 123 of the casing immediately above external cathodetermination 137 and immediately below the metal plating layers 65 a-65d. Of course, the present invention is by no means limited to the use ofconductive traces for forming the desired terminations, and any othersuitable means of connection can be employed. For instance, in someembodiments (not shown), it is to be understood that the portions of theanode lead frame and the cathode plating layers can extend through thecasing to also form the external anode termination and the externalcathode termination.

After connecting the capacitor elements 20 to the lower wall 123 asdiscussed above, the capacitor elements 20 can be coated with a resin orencapsulant material. In one particular embodiment, the encapsulantmaterial can be a thermally conductive material. Referring to FIG. 9,after the capacitor elements have been connected to the base 123 of thecapacitor assembly 100 in the desired manner, an encapsulant material143 can be disposed around the capacitor elements (not shown) such thatthe capacitor elements are at least partially encapsulated by theencapsulant material 143, after which the encapsulant material 143 canbe cured. Further, in some embodiments, the encapsulant material 143 cancompletely encapsulate the capacitor elements. Encapsulating thecapacitor elements with the encapsulant material 143 in such a mannercan further facilitate the ability of the capacitor assembly of thepresent invention to dissipate heat.

As noted above, the encapsulant material can be a thermally conductivematerial. The thermally conductive material, for instance, typically hasa thermal conductivity of about 1 W/m-K or more, in some embodimentsfrom about 2 W/m-K to about 20 W/m-K, and in some embodiments, fromabout 2.5 W/m-K to about 10 W/m-K, such as determined in accordance withISO 22007-2:2014. Despite being thermally conductive, the material isnot generally electrically conductive and thus has a relatively highvolume resistivity, such as about 1×10¹² ohm-cm or more, in someembodiments about 1×10¹³ ohm-cm or more, and in some embodiments, fromabout 1×10¹⁴ ohm-cm to about 1×10²⁰ ohm-cm, such as determined inaccordance with ASTM D257-14. Through the combination of a high thermalconductivity and low electrical conductivity, the present inventors havediscovered that the encapsulant material can provide a variety ofdifferent benefits when employed in a housing of the capacitor assembly.For example, when the capacitor assembly is exposed to a high ripplecurrent, the thermally conductive encapsulant material can act as a heattransfer sink that dissipates heat towards the surface of the housing,thus increasing cooling efficiency and the life of the capacitorassembly. The encapsulant material may also exhibit a low degree ofmoisture absorption, such as about 1% or less, in some embodiments about0.5% or less, and in some embodiments, about 0.1% or less, such asdetermined in accordance with ASTM D570-98(2010)e-1. In this manner, theencapsulant material can inhibit unwanted degradation reactions withwater that might enter the housing.

To help achieve the desired properties, the encapsulant materialcontains one or more thermally conductive fillers that are dispersedwithin a polymer matrix. Suitable thermally filler materials include,metallic fillers, such as aluminum, silver, copper, nickel, iron,cobalt, etc., as well as combinations thereof (e.g., silver-coatedcopper or silver-coated nickel); metal oxides, such as aluminum oxide,zinc oxide, magnesium oxide, etc., as well as combinations thereof;nitrides, such as aluminum nitride, boron nitride, silicon nitride,etc., as well as combinations thereof; and carbon fillers, such assilicon carbide, carbon black, carbon fullerenes, graphite flake, carbonnanotubes, carbon nanofibers, etc., as well as combinations thereof.Aluminum, zinc oxide, aluminum nitride, boron nitride, and/or silicacarbide powders may be particularly suitable for use in the presentinvention. If desired, the filler may be coated with a functionalcoating to improve the affinity between the filler and the polymermatrix. For example, such a coating may include an unsaturated orsaturated fatty acid, such as alkanoic acid, alkenoic acid, propionicacid, lauric acid, palmitic acid, stearic acid, etc.; organosilane,organotitanate, organozirconate, isocyanate, hydroxyl terminated alkeneor alkane, etc.

The size of the thermally conductive fillers may be selectivelycontrolled in the present invention to help achieve the desiredproperties. Generally speaking, such fillers have an average size (e.g.,diameter) of from about 10 nanometers to about 75 micrometers, in someembodiments from about 15 nanometers to about 50 micrometers, and insome embodiments, from about 20 nanometers to about micrometers. In someembodiments, the filler may have a nano-scale size, such as from about10 nanometers to about 500 nanometers, in some embodiments from about 20nanometers to about 350 nanometers, and in some embodiments, from about50 nanometers to about 200 nanometers, while in other embodiments, thefiller may have a micron-scale size, such as from about 1 micrometer toabout 50 micrometers, in some embodiments from about 2 micrometers toabout 30 micrometers, and in some embodiments, from about 5 micrometersto about 15 micrometers. The encapsulant material may also employ acombination of both nano-scale and micron-scale thermally conductivefillers. In such embodiments, the ratio of micron-scale filler to thenano-scale filler sized particle may be relatively large to ensure ahigh packing density, such as about 50:1 or more, and in someembodiments, from about 70:1 to about 150:1.

While a variety of different polymer resins may be employed in thematrix of the encapsulant material, curable thermosetting resins havebeen found to be particularly suitable for use in the present invention.Examples of such resins include, for instance, silicone polymers,diglycidal ethers of bishpenol A polymers, acrylate polymers, urethanepolymers, etc. In certain embodiments, for example, the encapsulantmaterial may employ one or more polyorganosiloxanes. Silicon-bondedorganic groups used in these polymers may contain monovalent hydrocarbonand/or monovalent halogenated hydrocarbon groups. Such monovalent groupstypically have from 1 to about 20 carbon atoms, preferably from 1 to 10carbon atoms, and are exemplified by, but not limited to, alkyl (e.g.,methyl, ethyl, propyl, pentyl, octyl, undecyl, and octadecyl);cycloalkyl (e.g., cyclohexyl); alkenyl (e.g., vinyl, allyl, butenyl, andhexenyl); aryl (e.g., phenyl, tolyl, xylyl, benzyl, and 2-phenylethyl);and halogenated hydrocarbon groups (e.g., 3,3,3-trifluoropropyl,3-chloropropyl, and dichlorophenyl). Typically, at least 50%, and moredesirably at least 80%, of the organic groups are methyl. Examples ofsuch methylpolysiloxanes may include, for instance, polydimethylsiloxane(“PDMS”), polymethylhydrogensiloxane, etc. Still other suitable methylpolysiloxanes may include dimethyldiphenylpolysiloxane,dimethyl/methylphenylpolysiloxane, polymethylphenylsiloxane,methylphenyl/dimethylsiloxane, vinyldimethyl terminatedpolydimethylsiloxane, vinylmethyl/dimethylpolysiloxane, vinyldimethylterminated vinylmethyl/dimethylpolysiloxane, divinylmethyl terminatedpolydimethylsiloxane, vinylphenylmethyl terminated polydimethylsiloxane,dimethylhydro terminated polydimethylsiloxane,methylhydro/dimethylpolysiloxane, methylhydro terminatedmethyloctylpolysiloxane, methylhydro/phenylmethyl polysiloxane, etc.

The organopolysiloxane may also contain one more pendant and/or terminalpolar functional groups, such as hydroxyl, epoxy, carboxyl, amino,alkoxy, methacrylic, or mercapto groups, which impart some degree ofhydrophilicity to the polymer. For example, the organopolysiloxane maycontain at least one hydroxy group, and optionally an average of atleast two silicon-bonded hydroxy groups (silanol groups) per molecule.Examples of such organopolysiloxanes include, for instance,dihydroxypolydimethylsiloxane,hydroxy-trimethylsiloxypolydimethylsiloxane, etc. Alkoxy-modifiedorganopolysiloxanes may also be employed, such asdimethoxypolydimethylsiloxane,methoxy-trimethylsiloxypolydimethylsiloxane,diethoxypolydimethylsiloxane,ethoxy-trimethylsiloxy-polydimethylsiloxane, etc. Still other suitableorganopolysiloxanes are those modified with at least one aminofunctional group. Examples of such amino-functional polysiloxanesinclude, for instance, diamino-functional polydimethylsiloxanes.

Desirably, the organopolysiloxane has a relatively low molecular weightto improve the viscosity and flow properties of the encapsulant materialprior to curing. In one embodiment, for example, the organopolysiloxane(e.g., polydimethylsiloxane) has a molecular weight of about 100,000g/mole or less, in some embodiments about 60,000 g/mole or less, and insome embodiments, from about 5,000 to about 30,000 g/mole. The resultingviscosity of the encapsulant material (prior to curing) may be, forexample, about 500 Pa-s or less, in some embodiments about 100 Pa-s orless, and in some embodiments, from about 1 to about 50 Pa-s, such asdetermined at a temperature of 25° C. using an ARES R550PS stresscontrolled rheometer equipped with a 20-mm parallel plate set at a 0.5mm gap.

The relative amount of thermally conductive fillers and the polymermatrix may be selectively controlled so that the desired properties areachieved. For example, the encapsulant material typically contains fromabout 25 vol. % to about 95 vol. %, in some embodiments from about 40vol. % to about 90 vol. %, and in some embodiments, from about 50 vol. %to about 85 vol. %. Likewise, the polymer matrix may constitute fromabout 5 vol. % to about 75 vol. %, in some embodiments from about 10vol. % to about 50 vol. %, and in some embodiments, from about 15 vol. %to about 40 vol. % of the material. If desired, other additives may alsobe employed in the encapsulant material, such as compatibilizers, curingagents, photoinitiators, viscosity modifiers, pigments, coupling agents(e.g., silane coupling agents), stabilizers, etc.

Once assembled and connected in the desired manner, the resultingpackage is hermetically sealed as described above. Referring again toFIG. 1, for instance, the housing may also include a lid 127 that isplaced on an upper surface of side walls 124 and 125 after the capacitorelements are positioned within the housing. The lid may be formed from aceramic, metal (e.g., iron, copper, nickel, cobalt, etc., as well asalloys thereof), plastic, and so forth. If desired, a sealing member(not shown) may be disposed between the lid and the side walls 124 and125 to help provide a good seal. In one embodiment, for example, thesealing member may include a glass-to-metal seal, Kovar® ring(Goodfellow Camridge, Ltd.), etc. The height of the side walls isgenerally such that the lid does not contact any surface of thecapacitor elements so that they are not contaminated. When placed in thedesired position, the lid is hermetically sealed to the sidewalls 124and 125 using known techniques, such as welding (e.g., resistancewelding, laser welding, etc.), soldering, etc. Hermetic sealing can, insome embodiments, occur in the presence of inert gases as describedabove so that the resulting assembly is substantially free of reactivegases, such as oxygen or water vapor.

In the embodiments shown in FIGS. 4-6, the capacitor assembly includes40 capacitor elements. However, as noted above, any number of capacitorelements may generally be employed in the present invention, such asabout 2 to about 200, in some embodiments from about 10 to about 100,and in some embodiments, from about 20 to about 50.

Regardless of its particular configuration, the capacitor assembly ofthe present invention may exhibit excellent electrical properties evenwhen exposed to high voltage environments and increased temperatures.For example, due to the ability of the capacitor assembly of the presentinvention to dissipate heat, relatively high ripple currents may beachieved without damaging the capacitor assembly. For example, themaximum ripple current may be about 25 Amps or more, in someembodiments, about 50 Amps or more, and in some embodiments, about 75Amps or more. Further, the equivalent series resistance (ESR) of thecapacitor assembly may be less than about 50 milliohms, in someembodiments less than about 25 milliohms, and in some embodiments, lessthan about 10 milliohms. For instance, the ESR can range from about 0.5milliohms to about 10 milliohms, such as from about 1 milliohm to about8 milliohms, such as from about 2 milliohms to about 6 milliohms.

The present invention may be better understood by reference to thefollowing example.

Test Procedures Equivalent Series Resistance (ESR)

Equivalence series resistance may be measured using an Agilent E4980APrecision LCR Meter with Kelvin Leads 2.2 volt DC bias and a 0.5 voltpeak to peak sinusoidal signal. The operating frequency was 100 kHz andthe temperature was 23° C.±2° C.

Capacitance (CAP)

The capacitance was measured using an Agilent E4980A Precision LCR Meterwith Kelvin Leads with 2.2 volt DC bias and a 0.5 volt peak to peaksinusoidal signal. The operating frequency was 120 Hz.

Leakage Current (DCL)

Leakage current was measured using a Keithley 2410 Source Meter measuresleakage current at an appropriate voltage (Ur for 25° C.-85° C., 60% ofUr for 125° C. and 50% of Ur for 150° C.) after a minimum of 60 seconds.

Ripple Current:

Ripple current was measured using a GoldStar GP 505 power supply, anAgilent 33210A signal generator, an Almemo 2590-9 data logger with Pt100thermocouples, and a Fluke 80i oscilloscope. The operating frequency was20 kHz with AC signal and 10 volt DC bias when the appropriate value ofripple current was passed through the capacitor. With increasing ripplecurrent, the temperature also increased and was monitored via athermocamera.

Example

9,000 μFV/g tantalum powder was used to form anode samples. Each anodesample was embedded with a tantalum wire, sintered at 1800° C., andpressed to a density of 5.3 g/cm³. The resulting pellets had a size of4.6 mm×5.25 mm×2.6 mm. The pellets were anodized to 260V in awater/phosphoric acid electrolyte with a conductivity of 8.6 mS at atemperature of 85° C. to form the dielectric layer. A conductive polymercoating was then formed by dipping the anodes into a dispersion ofpoly(3,4-ethylenedioxythiophene) having a solids content of 1.1% and aviscosity of 20 mPa·s (Clevios™ K, H. C. Starck). Upon coating, theparts were dried at 125° C. for 20 minutes. This process was repeatedtimes. Thereafter, the parts were dipped into a dispersion ofpoly(3,4-ethylenedioxythiophene) having a solids content of 2% and aviscosity of 20 mPa·s (Clevios™ K, H. C. Starck). Upon coating, theparts were dried at 125° C. for 20 minutes. This process was notrepeated. Next, the parts were dipped into a dispersion ofpoly(3,4-ethylenedioxythiophene) having a solids content of 2% andviscosity of 160 mPa·s (Clevios™ K, H. C. Starck). Upon coating, theparts were dried at 125° C. for 20 minutes. This process was repeated 8times. The parts were then dipped into a graphite dispersion and dried.Finally, the parts were dipped into a silver dispersion and dried.Multiple parts of 100V capacitors were made in this manner.

A copper-based lead frame material was used to finish the assemblyprocess to place the capacitor elements into a ceramic housing. Thecapacitor assembly included 36 capacitor elements connected in parallelin 4 rows (9 capacitor elements per row). The cathode connective memberswere then glued to a nickel cathode termination and the anode lead framewas welded to a nickel anode termination at a lower wall of a ceramichousing having a length of 58.0 mm, a width of 35.0 mm, and a thicknessof 5.45 mm. The housing had nickel plated NILO® solder pads solderedonto an inner surface of the lower wall of the ceramic housing.

The adhesive employed for all connections was a silver paste. Theassembly was then loaded in a convection oven to solder the paste. Afterthat, the welding employed for the anode connection was a resistancewelding using 300 W of energy that was applied between the lead frameportions and ceramic housing nickel plated solder pad for a time periodof 100 ms. Then, a thermally conductive silicone encapsulant (ThermosetSC-320) was applied over the top of the anode and cathode portions ofthe capacitor elements and was dried at 150° C. for 24 hours. Next, aKovar® lid was placed over the top of the housing, closely on the sealring of the ceramic. The resulting assembly was placed into a weldingchamber and purged with nitrogen gas before seam welding between theseal ring and the lid was performed.

After testing, it was determined that the capacitance was 340.1 μF,while the ESR was 4.3 mΩ. A summary of the leakage current and ripplecurrent test results are shown below.

Leakage Current Characteristics of Example Temperature DCL (μA) @ DCL(μA) @ [° C.] 60 s 300 s −55 5.09 0.12 25 5.72 0.98 85 29.57 8.06 12517.88 5.95 150 35.92 11.73

Peak-to-peak Current @ RMS Current Temperature 20 kHz @ 20 kHz [° C.] I(Amps) I (Amps) 31.8 5.0 3.54 36.3 10.0 7.07 49.7 15.0 10.61 71.0 20.014.14 103.6 25.0 17.68

As shown, the capacitor assembly made according the Example was able towithstand 25 Amps of ripple current and only reached a temperature of103.6° C.

These and other modifications and variations of the present inventionmay be practiced by those of ordinary skill in the art, withoutdeparting from the spirit and scope of the present invention. Inaddition, it should be understood that aspects of the variousembodiments may be interchanged both in whole or in part. Furthermore,those of ordinary skill in the art will appreciate that the foregoingdescription is by way of example only, and is not intended to limit theinvention so further described in such appended claims.

What is claimed is:
 1. A capacitor assembly comprising: a plurality ofcapacitor elements that each contain a sintered porous anode body, adielectric layer that overlies the anode body, and a solid electrolyteoverlying the dielectric layer, wherein an anode lead extends from eachcapacitor element, wherein each capacitor element is defined by upperand lower major surfaces, first opposing minor surfaces, and secondopposing minor surfaces, wherein the upper and lower major surfaces eachhave a surface area that is greater than a surface area of each of theminor opposing surfaces; a housing having a length, a width, and aheight, wherein the ratio of the length to the height ranges from about2 to about 80, wherein the housing is hermetically sealed and defines aninterior cavity within which the plurality of capacitor elements arepositioned, wherein the lower major face of each capacitor element facesa lower wall of the housing, further wherein the lower wall is definedby the length and the width of the housing; an external anodetermination that is in electrical connection with the anode lead of eachcapacitor element; and an external cathode termination that is inelectrical connection with the solid electrolyte of each capacitorelement.
 2. The capacitor assembly of claim 1, wherein the interiorcavity has a gaseous atmosphere that contains an inert gas.
 3. Thecapacitor assembly of claim 1, wherein the housing is formed from ametal, plastic, ceramic, or a combination thereof.
 4. The capacitorassembly of claim 1, further comprising an anode lead frame thatconnects the anode lead of each capacitor element with the externalanode termination.
 5. The capacitor assembly of claim 1, wherein thesolid electrolyte is electrically connected to the external cathodetermination via a conductive adhesive.
 6. The capacitor assembly ofclaim 1, wherein the capacitor elements are arranged in multipleparallel rows, wherein each row of capacitor elements extends in alongitudinal direction along the length of the housing.
 7. The capacitorassembly of claim 1, wherein the capacitor assembly includes from 2 toabout 200 capacitor elements.
 8. The capacitor assembly of claim 1,wherein the plurality of capacitor elements are connected in parallel.9. The capacitor assembly of claim 1, wherein the height of the housingranges from about 1 millimeter to about 20 millimeters.
 10. Thecapacitor assembly of claim 1, wherein the ratio of the total surfacearea of the lower major surfaces of the capacitor elements to the volumeof the housing ranges from about 0.06 mm¹ to about 0.3 mm⁻¹.
 11. Thecapacitor assembly of claim 1, wherein the anode body is formed from apowder that contains tantalum, niobium, or an electrically conductiveoxide thereof.
 12. The capacitor assembly of claim 1, wherein the solidelectrolyte includes a conductive polymer or manganese dioxide.
 13. Thecapacitor assembly of claim 12, wherein the conductive polymer is asubstituted polythiophene.
 14. The capacitor assembly of claim 13,wherein the substituted polythiophene ispoly(3,4-ethylenedioxythiophene).
 15. The capacitor assembly of claim 1,wherein the solid electrolyte comprises a plurality of pre-polymerizedconductive polymer particles.
 16. The capacitor assembly of claim 1,wherein the capacitor assembly has a maximum ripple current of about 25Amps or more.
 17. The capacitor assembly of claim 1, wherein thecapacitor assembly has an equivalent series resistance of less thanabout 10 milliohms.
 18. The capacitor assembly of claim 1, wherein anencapsulant material at least partially encapsulates the plurality ofcapacitor elements.
 19. The capacitor assembly of claim 18, wherein theencapsulant material is thermally conductive.
 20. The capacitor assemblyof claim 19, wherein the encapsulant material has a thermal conductivityof about 1 W/m-K or more.